September 11, 2006

Climate Science Abuzz over Fly Genetics

Filed under: Adaptation, Animals

(alternative title: Bad News for Future Bananas)

So what do you think? Is it good news that a species adapts to climate change or not? Given that evolution is a fact, should it even be news at all? Or should some nice, cuddly species adapt (e.g., koala bears, owls, baby seals) but not others (e.g., Colorado potato beetles, hissing cockroaches)?

An article published in Science Express makes the case that a species of fruit fly (Drosophila subobscura) has adapted to warming on three continents in a relatively short period of time. Joan Balanya from the University of Barcelona and three colleagues tracked genetic changes in this species of fruit fly in Europe, North America, and South America. They compared chromosome arrangements in 26 fly populations from previous studies completed 13 to 46 years ago to recent samples and identified genetic changes, called “chromosome inversion frequencies.” They correlated these changes with mean monthly weather data taken four years prior to the original study to a current four-year period that coincides with more contemporary samples.

The authors noted “Drosophila subobscura is experiencing detectable climate warming on three continents. Environmental warming appears to have made a genetic impact on these flies, as frequencies of chromosome inversions associated with warm latitudes have increased in parallel with climate on these continents.”

So if this study is correct, here is another piece of evidence that species adapt to their environment. The reverse conclusion would actually be surprising. Good new for fruit flies, no doubt, but not Science material. Of course, alert global warming aficionados know that there has to be a kicker, so here goes:

“The increasing numbers of examples documenting genetic as well as phenotypic responses to recent climate change are not surprising from an evolutionary perspective, but nonetheless are disturbing from ecological or economic ones, because such changes signal inevitable disruptions in the distributions, population dynamics, and community interactions of organisms.”

The contextual equivalent of that sentence can be found in almost all global warming papers published in Science. From June 1, 2005, through July 31, 2006, Science published 34 global warming articles saying things are worse than we thought, and only 4 saying it’s not so bad. Given that science is supposed to be neutral, this is profound evidence for what is known as “Publication Bias.” Such a disparity could only arise by chance in an unbiased world about one in a million times.

But, it’s the necessary sentence that thrusts the manuscript over the publication threshold—the reminder that global warming is here and it’s bad.

Here, we propose a slightly revised, but equally valid conclusion:

The increasing numbers of examples documenting genetic as well as phenotypic responses to recent climate change are not surprising from an evolutionary perspective and are an encouraging sign that species can and will adapt, often rapidly, to ambient environmental changes.

That change in the conclusion—the opinion of the authors completely unrelated to the quality of the research—would almost certainly kick this paper into Science magazine’s reject pile. According to our recent review of the Science magazine’s contents, the odds are very long that a research paper suggesting that climate change is not an impending disaster will make it into Science. Many such papers have been published in other, good, journals, just not very often in Science.

Back to fruit flies. The problem with this kind of research is the risk of false correlation. Over the last 20-40 years, many places on Earth have been warming. But obviously warming is not responsible for the increase in every observable phenomenon on the planet (although, more and more, it seems people are acting that way). The correlation between the first principal component of chromosome arrangement frequencies in 26 fruit fly communities on three continents with the first principal component of average monthly temperature does not prove cause-and-effect.

While it’s not clear if flies migrated from warmer latitudes or if natural selection preferred individual flies adapted to warmer conditions, there is evidence of adaptation in either case. But if flies are really adapting to higher temperatures, which is not only reasonable, but likely, what’s the catch? For the proper spin, coverage in NewScientist.com notes that flies, which pass through several generations per year, will adapt faster than sequoia trees. Or as University of Texas biologist Camille Parmesan noted, this research is a warning that species may only have limited ability to adapt within their own genome.

How about a little reality check. Over the long course of history during which this species of fruit fly has existed, it has faced far greater temperature changes than the comparatively minor ones seen over the last few decades, and it apparently has survived just fine. It did this via evolutionary adaptation. Species that can adapt to climate change will do so, ones that can’t, won’t. Basic Darwinian reality. If for some reason this process stops, then you’ve really got a paper worthy of Science, or perhaps even some other, quality, journal.

Reference:

Balanya, J., J.M. Oller, R.B. Huey, G.W. Gilchrist, and L. Serra, 2006. Global genetic change tracks global climate warming, Sciencexpress, 31 August 20062006/10.1126/science.1131002.




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